Quick Reference Guide to 10-Mbps Multi-Segment Configuration

Next, let's look at a more complex example. In this example we're going to encounter lots of different segment types, extra AUI cables, etc. Be warned that all these extra bits and pieces make the example much more complex to explain, although the basic process of looking up the bit times and adding them together is still quite simple. Nonetheless, for the next several pages I will be droning on and on about extra delay times for AUI cables, swapping left and right end segments, and so on. If you aren't interested in evaluating a more complex network you may want to stop reading at this point.

Refer back to Figure 7.3, which shows one possible maximum-length system using four repeaters and five segments. As we've seen, the rule-based configuration method shows that this system is OK. To check that, we'll evaluate the same system using the calculation method provided in Model 2.

We start by finding the worst-case path in the sample network. By examination, you can see that the path in Figure 7.3 between DTE1 and DTE2 is the maximum delay path, since it contains the largest number of segments and repeaters in the path between any two DTEs in the network. Next, we make a network model out of the worst-case path. Let's start the process by assigning the thin Ethernet end segment to be the left end segment. That leaves us with three middle segments composed of a 10BASE5 segment and two fiber optic link segments, and a right end segment composed of a 10BASE-T link segment.

Next, we find out what the segment delay value is for a 10BASE2 left end segment. We could calculate the segment delay value by adding the left end base value for 10BASE2 coax (11.75) to the product of the round trip delay times the length in meters (185 * 0.1026 = 18.981) to come up with a total segment delay value of 30.731 for the thin coax segment. However, since 185 meters is the maximum segment length allowed for 10BASE2 segments, we can simply look up the Max left hand segment value in the table, which, not surprisingly, is 30.731.

The 10BASE2 thin Ethernet segment is shown attached directly to the DTE and repeater, and there is no AUI cable in use. Therefore, we don't have to add any "excess AUI" cable length timing to the value for this segment.

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